The present invention relates to refrigerant compressors and, more particularly, to a bearing lubricating structure of a refrigerant compressor, which intends to improve the wear resistance of a bearing, and its associated parts on a suction side of the compressor.
A vane compressor in general is simple in structure and suitable for high rotational speed operation, and has therefore widely been used as a refrigerant compressor in an air conditioning system for vehicles. The refrigerant compressor is one of components realizing a steam refrigerating cycle which employs, as operating fluid, refrigerant such as flon. The refrigerant compressor compresses the flon gas evaporated by an evaporator and supplies the compressed flon gas to a condenser by which the flon gas is condensed.
In the refrigerant compressor of the kind referred to above, the refrigerant contains lubricating oil for lubrication of various portions of the compressor. Recently, needle roller bearings are mainly employed as radial bearings for rotatably supporting a driving shaft, in order to improve their resistance to seizure.
However, if the refrigerant compressor is operated at idling for a long period of time while the air conditioning system is in a low thermal condition, the needle roller bearing on the suction side of the refrigerant compressor and its vicinity are subjected to low temperature and high pressure (35.degree. to 36.degree. C. and 8 atg, for example), so that the refrigerant around the needle roller bearing is in a wet or steamy state. Thus, the lubricating oil on the needle roller bearing is diluted with the wet or steamy refrigerant to be reduced in viscosity. FIG. 3 graphically shows a change in viscosity of naphthenic lubricating oil as an example, with the abscissa indicating the percentage of flon (R-12 according to Japan Industrial Standard) solved in the lubricating oil in terms of weight percent (Wt %), and the ordinate indicating the viscosity of the lubricating oil in terms of centistoke (cSt) and in logarithmic scale.
In general, the service life of a bearing of this kind depends upon the thickness of oil film thereon. Since the oil film thickness is in proportion to the 0.736th power of the viscosity of the lubricating oil, it is necessary to suppress or restrain the dilution of the lubricating oil with the wet or steamy refrigerant, in order to enhance the seizure resistance and wear resistance of the bearing and its peripheral parts for prolonging the service life of the bearing.